1. Field of the Invention
This invention relates to microfluidic systems for handling or processing fluid suspensions of dielectric particles including living cells, spores, viruses, polymer beads, and aggregates of macromolecules. In particular, the invention involves the use of dielectrophoresis (DEP) induced forces to manipulate or control the velocity, including direction, of dielectric particles in microfluidic devices. The invention can be employed in a wide variety of applications including, but not limited to, the processing, separation and/or concentration of analyte mixture components containing living, non-living, transformed, and/or malfunctioning cells, polymer beads, bacterial or fungal spores, and macromolecules. This invention is capable of separating and concentrating particles based on particle size as well as the electrical properties of the particles.
2. Description of Related Art
The manipulation of particulate fluid suspensions in microfluidic systems, including suspensions of cells and microbes, by applied dielectrophoresis (DEP) forces is known in the art. Reviews of dielectrophoretic manipulation and separation of particles in a microfluidic environment are presented in the following references: GASCOYNE et al. (2004) “Dielectrophoresis-Based Sample Handling in General-Purpose Programmable Diagnostic Instruments” Proceedings of the IEEE 92(1):22-42; MÜLLER et al. (2003) “The Potential of Dielectrophoresis for Single-Cell Experiments” IEEE Engineering in Medicine and Biology Magazine 22(6):51-61; and WONG et al. (2004) “Electrokinetics in Micro Devices for Biotechnology Applications” IEEE/ASME Transactions on Mechatronics 9(2): 366-376, which are incorporated by reference in their entirety.
The direction and magnitude of DEP forces acting on suspended particles depend on particle size, the electric properties of the particles and suspending fluid (medium), and the magnitude, frequency, and waveform of the imposed electric field. The magnitude of the imposed electric field depends on the applied voltage and distance between electrodes. Two types of DEP forces act on particles: (a) conventional DEP (c-DEP) forces that are proportional to the gradient of the electric field strength, and (b) traveling wave DEP (tw-DEP) forces that are proportional to the gradient of the phase of an applied Alternating Current (AC) electric field signal. A c-DEP force tends to move particles to regions where an electric field is either at a minimum (negative DEP) or maximum (positive DEP), depending on the frequency of the signal, and the material properties of the suspending fluid and particles. A Direct Current (DC) electric field is sufficient to induce c-DEP forces while a phase-alternating AC field is required to induce tw-DEP. Accordingly, multiple electrodes must be used to generate tw-DEP. The theoretical foundations of DEP forces and their quantitative descriptions can be found in “Electromechanics of Particles” by Thomas B. Jones, published in 1995 by Cambridge University Press. DEP forces generated by applying DC and AC fields to a pair of interdigitated electrodes located at the bottom of a separation chamber are described by FENG et al. (2002) “Numerical and Analytical Studies of AC Electric Field in Dielectrophoretic Electrode Arrays” Proceedings of the 2002 International Conference on Computational Nanoscience and Nanotechnology, 2:85-88.
A particle experiences conventional DEP forces when a non-uniform electric field is established in the suspending medium upon energizing the electrodes with a DC and/or AC electric field. These c-DEP forces have two components: a normal component that levitates the particle in a direction normal to the electrode surfaces and a horizontal (lateral) component that pushes the particle away from electrodes. Both components of c-DEP forces decrease significantly as the particle is moved away from the electrode.
Conventional microfluidic DEP systems may be exemplified by GASCOYNE and VYKOUKAL (2004) Proceedings of the IEEE 92(1):22-42), U.S. Pat. No. 6,310,309 B1 (AGER et al.), and U.S. Pat. No. 6,749,736 B1 (FUHR et al.), which are incorporated by reference in their entirety. Each of these systems suffers from one or more disadvantages relating to their durability, capacity, and/or functional flexibility with regard to programmability and multipurpose functionality, for example.
The present invention uses arrangements of electrodes that have been designed based on high-fidelity, ab initio physics-based simulations. The electrode arrangement designs have been used to fabricate and engineer microfluidic devices that achieve programmable, high efficiency particle separations at relatively high fluid flow rates. The electrodes are arranged to provide high DEP forces using voltages that do not damage living cells, for example, and permit larger channel dimensions and higher flow volumes than existing microfluidic DEP devices. The present invention also encompasses high throughput systems in which separation chambers are arranged in parallel or series and higher efficiency systems in which samples are recycled through one or more separation chambers.